The Experts below are selected from a list of 7974 Experts worldwide ranked by ideXlab platform
Libbrecht, Kenneth G. - One of the best experts on this subject based on the ideXlab platform.
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Triangular Snowflakes: Growing Structures with Three-fold Symmetry using a Hexagonal Ice Crystal Lattice
2021Co-Authors: Libbrecht, Kenneth G.Abstract:Snow crystals growing from water vapor occasionally exhibit morphologies with three-fold (trigonal) symmetry, even though the ice crystal lattice has a molecular structure with six-fold symmetry. In extreme cases, thin platelike snow crystals can grow into faceted forms that resemble simple equilateral triangles. Although far less common than hexagonal forms, trigonal snow crystals have long been observed both in nature and in laboratory studies, and their origin has been an enduring scientific puzzle. In this paper I describe how platelike trigonal structures can be grown on the ends of slender ice needles in air with high reliability at -14 C. I further suggest a physical model that describes how such structures can self-assemble and develop, facilitated by an edge-sharpening instability that turns on at a specific combination of temperature and water-vapor supersaturation. The results generally support a comprehensive model of structure-dependent Attachment Kinetics in ice growth that has been found to explain many of the overarching behaviors seen in the Nakaya diagram of snow crystal morphologies
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Toward a Comprehensive Model of Snow Crystal Growth: 7. Ice Attachment Kinetics near -2 C
2020Co-Authors: Libbrecht, Kenneth G.Abstract:I examine a variety snow crystal growth experiments performed at temperatures near -2 C, as a function of supersaturation, background gas pressure, and crystal morphology. Although the different experimental data were obtained using quite diverse experimental techniques, the resulting measurements can all be reasonably understood using a single comprehensive physical model for the basal and prism Attachment Kinetics, together with particle diffusion of water vapor through the surrounding medium and other well-understood physical processes. As with the previous paper in this series, comparing and reconciling different data sets at a single temperature yields significant insights into the underlying physical processes that govern snow crystal growth dynamics
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Toward a Comprehensive Model of Snow Crystal Growth: 8. Characterizing Structure-Dependent Attachment Kinetics near -14 C
2020Co-Authors: Libbrecht, Kenneth G.Abstract:In this paper I examine snow crystal growth near -14 C in comparison with a comprehensive model that includes Structure-Dependent Attachment Kinetics (SDAK). Analyzing a series of ice-growth observations in air, I show that the data strongly support the model, which stipulates that basal growth is described by classical terrace nucleation on faceted surfaces in this temperature region. In contrast, prism growth exhibits a pronounced "SDAK dip" that substantially reduces the nucleation barrier on narrow prism facets (relative to that found on broad prism facets). I use these measurements to further characterize and refine the SDAK model, which effectively explains the robust formation of platelike snow crystals in air near 14 C
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Toward a Comprehensive Model of Snow Crystal Growth: 9. Characterizing Structure-Dependent Attachment Kinetics near -4 C
2020Co-Authors: Libbrecht, Kenneth G.Abstract:In this paper I examine snow crystal growth near -4 C in comparison with a comprehensive model that includes Structure-Dependent Attachment Kinetics (SDAK). Together with the previous paper in this series that investigated growth near 14 C, I show that a substantial body of experimental data now supports the existence of pronounced 'SDAK dips' on basal surfaces near -4 C and on prism surfaces near -14 C. In both cases, the model suggests that edge-associated surface diffusion greatly reduces the nucleation barrier on narrow facet surfaces relative to that found on broad facets. The remarkable quantitative similarities in the growth behaviors near -4 C and -14 C suggest that these two SDAK features arise from essentially the same physical mechanism occurring at different temperatures on the two principal facets. When applied to atmospheric snow crystal formation, this comprehensive model can explain the recurrent morphological transitions between platelike and columnar growth seen in the Nakaya diagram
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Toward a Comprehensive Model of Snow Crystal Growth: 6. Ice Attachment Kinetics near -5 C
2019Co-Authors: Libbrecht, Kenneth G.Abstract:I examine a variety of snow crystal growth measurements taken at a temperature of -5 C, as a function of supersaturation, background gas pressure, and crystal morphology. Both plate-like and columnar prismatic forms are observed under different conditions at this temperature, along with a diverse collection of complex dendritic structures. The observations can all be reasonably understood using a single comprehensive physical model for the basal and prism Attachment Kinetics, together with particle diffusion of water vapor through the surrounding medium and other well-understood physical processes. A critical model feature is structure-dependent Attachment Kinetics (SDAK), for which the molecular Attachment Kinetics on a faceted surface depend strongly on the nearby mesoscopic structure of the crystal
Josh E Baker - One of the best experts on this subject based on the ideXlab platform.
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velocity of myosin based actin sliding depends on Attachment and detachment Kinetics and reaches a maximum when myosin binding sites on actin saturate
Journal of Biological Chemistry, 2021Co-Authors: Travis J Stewart, Vidya Murthy, Sam P Dugan, Josh E BakerAbstract:Abstract Molecular motors such as kinesin and myosin often work in groups to generate the directed movements and forces critical for many biological processes. Although much is known about how individual motors generate force and movement, surprisingly little is known about the mechanisms underlying the macroscopic mechanics generated by multiple motors. For example, the observation that a saturating number, N, of myosin heads move an actin filament at a rate that is influenced by actin-myosin Attachment and detachment Kinetics is accounted for neither experimentally nor theoretically. To better understand the emergent mechanics of actin-myosin mechanochemistry, we use an in vitro motility assay to measure and correlate the N-dependence of actin sliding velocities, actin-activated ATPase activity, force generation against a mechanical load, and the calcium sensitivity of thin filament velocities. Our results show that velocity and ATPase activity are both strain-dependent, and that velocity becomes maximized with the saturation of myosin binding sites on actin at a value that is 40% dependent on Attachment Kinetics and 60% dependent on detachment Kinetics. These results support a chemical thermodynamic model for ensemble motor mechanochemistry and imply molecularly explicit mechanisms within this framework, challenging the assumption of independent force generation.
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actin sliding velocities are influenced by actin myosin Attachment Kinetics
Biophysical Journal, 2011Co-Authors: Del R Jackson, Travis J Stewart, Alan Stickney, Josh E BakerAbstract:Unloaded muscle shortening velocities (V) are widely thought to be limited by actin-myosin detachment Kinetics (Ton); however, recent studies indicate that actin-myosin Attachment Kinetics (katt) significantly influence V. To test the hypothesis that V varies with katt, we use stopped flow fluorescence spectrometry to study effectors of katt and in vitro motility assays to correlate observed effects on katt with changes in V. Here we consider the combined effects of sucrose and potassium chloride, KCl. We show that sucrose specifically inhibits the rate of actin-myosin binding, katt, and the effects of sucrose on katt correlate with its effects on V. Moreover, the addition of KCl enhances the effects of sucrose on katt, with the combined effects of KCl and sucrose on katt mirroring their effects on V, suggesting that the ionic strength-dependence of katt contributes to the ionic strength-dependence of V. We are investigating mechanisms by which both KCl and sucrose influence katt, and we have developed a collective force model that accounts for the observed influence of both katt and Ton on V. Our data and model imply that factors that decrease katt such as regulatory proteins, certain disease related mutations, and inhibitors such as blebbistatin can slow V through kinetic rather than recruitment or sequestration mechanisms.
Marcello Lappa - One of the best experts on this subject based on the ideXlab platform.
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an Attachment Kinetics based level set method for macromolecular crystallization under buoyancy driven convective effects
International Journal of Computational Fluid Dynamics, 2004Co-Authors: Marcello LappaAbstract:A level-set method, specifically conceived for the case of organic crystal growth from supersaturated solutions, is introduced and described in detail. The model can simulate the growth due to the slow addition of solute molecules to the surface of a lattice and can handle the shape of macromolecular growing crystals under the influence of natural convection. It is carefully developed according to the complex properties and mechanisms of protein crystal growth taking into account the possibility of anisotropic growth due to either “faceted” surface-orientation-dependent behaviors or the influence of external convection occurring in the protein reactor. The analogies and differences between this technique and a previous volume of fraction method are discussed in terms of theoretical aspects and fundamental equations. The advantages and limitations of both formulations are pointed out.
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An "Attachment Kinetics-based" volume of fraction method for organic crystallization: a fluid-dynamic approach to macromolecular-crystal engineering
Journal of Computational Physics, 2003Co-Authors: Marcello LappaAbstract:This analysis exhibits a strong interdisciplinary nature and deals with advances in protein (crystal) engineering models and computational methods as well as with novel results on the relative importance of 'controlling forces' in macromolecular crystal growth. The attention is focused in particular on microgravity fluid-dynamic aspects. From a numerical point of view, the growing crystal gives rise to a moving boundary problem. A 'kinetic-coefficient-based' volume tracking method is specifically and carefully developed according to the complex properties and mechanisms of macromolecular protein crystal growth taking into account the possibility of anisotropic (faceted) surface-orientation-dependent growth. The method is used to shed some light on the interplay of surface Attachment Kinetics and mass transport (diffusive or convective) in liquid phase and on several mechanisms still poorly understood. It is shown that the size of a growing crystal plays a 'critical role' in the relative importance of surface effects and in determining the intensity of convection. Convective effects, in turn, are found to impact growth rates, macroscopic structures of precipitates, particle size and morphology as well as the mechanisms driving growth. The paper introduces a novel computational method (that simulates the growth due to the slow addition of solute molecules to a lattice and can handle the shape of organic growing crystals under the influence of natural convection) and, at the same time, represents a quite exhaustive attempt to help organic crystal growers to discern the complex interrelations among the various parameters under one's control (that are not independent of one another) and to elaborate rational guidelines relating to physical factors that can influence the probability of success in crystallizing protein substances.
Travis J Stewart - One of the best experts on this subject based on the ideXlab platform.
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velocity of myosin based actin sliding depends on Attachment and detachment Kinetics and reaches a maximum when myosin binding sites on actin saturate
Journal of Biological Chemistry, 2021Co-Authors: Travis J Stewart, Vidya Murthy, Sam P Dugan, Josh E BakerAbstract:Abstract Molecular motors such as kinesin and myosin often work in groups to generate the directed movements and forces critical for many biological processes. Although much is known about how individual motors generate force and movement, surprisingly little is known about the mechanisms underlying the macroscopic mechanics generated by multiple motors. For example, the observation that a saturating number, N, of myosin heads move an actin filament at a rate that is influenced by actin-myosin Attachment and detachment Kinetics is accounted for neither experimentally nor theoretically. To better understand the emergent mechanics of actin-myosin mechanochemistry, we use an in vitro motility assay to measure and correlate the N-dependence of actin sliding velocities, actin-activated ATPase activity, force generation against a mechanical load, and the calcium sensitivity of thin filament velocities. Our results show that velocity and ATPase activity are both strain-dependent, and that velocity becomes maximized with the saturation of myosin binding sites on actin at a value that is 40% dependent on Attachment Kinetics and 60% dependent on detachment Kinetics. These results support a chemical thermodynamic model for ensemble motor mechanochemistry and imply molecularly explicit mechanisms within this framework, challenging the assumption of independent force generation.
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actin sliding velocities are influenced by actin myosin Attachment Kinetics
Biophysical Journal, 2011Co-Authors: Del R Jackson, Travis J Stewart, Alan Stickney, Josh E BakerAbstract:Unloaded muscle shortening velocities (V) are widely thought to be limited by actin-myosin detachment Kinetics (Ton); however, recent studies indicate that actin-myosin Attachment Kinetics (katt) significantly influence V. To test the hypothesis that V varies with katt, we use stopped flow fluorescence spectrometry to study effectors of katt and in vitro motility assays to correlate observed effects on katt with changes in V. Here we consider the combined effects of sucrose and potassium chloride, KCl. We show that sucrose specifically inhibits the rate of actin-myosin binding, katt, and the effects of sucrose on katt correlate with its effects on V. Moreover, the addition of KCl enhances the effects of sucrose on katt, with the combined effects of KCl and sucrose on katt mirroring their effects on V, suggesting that the ionic strength-dependence of katt contributes to the ionic strength-dependence of V. We are investigating mechanisms by which both KCl and sucrose influence katt, and we have developed a collective force model that accounts for the observed influence of both katt and Ton on V. Our data and model imply that factors that decrease katt such as regulatory proteins, certain disease related mutations, and inhibitors such as blebbistatin can slow V through kinetic rather than recruitment or sequestration mechanisms.
B J Berne - One of the best experts on this subject based on the ideXlab platform.
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interface limited growth of heterogeneously nucleated ice in supercooled water
Journal of Physical Chemistry B, 2014Co-Authors: Razvan A Nistor, Thomas E Markland, B J BerneAbstract:Heterogeneous ice growth exhibits a maximum in freezing rate arising from the competition between Kinetics and the thermodynamic driving force between the solid and liquid states. Here, we use molecular dynamics simulations to elucidate the atomistic details of this competition, focusing on water properties in the interfacial region along the secondary prismatic direction. The crystal growth velocity is maximized when the efficiency of converting interfacial water molecules to ice, collectively known as the Attachment Kinetics, is greatest. We find water molecules that contact the intermediate ice layer in concave regions along the atomistically roughened surface are more likely to freeze directly. An increased roughening of the solid surface at large undercoolings consequently plays an important limiting role in the rate of ice growth, as water molecules are unable to integrate into increasingly deeper surface pockets. These results provide insight into the molecular mechanisms for self-assembly of solid...
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interface limited growth of heterogeneously nucleated ice in supercooled water
arXiv: Soft Condensed Matter, 2013Co-Authors: Razvan A Nistor, Thomas E Markland, B J BerneAbstract:Heterogeneous ice growth exhibits a maximum in freezing rate arising from the competition between Kinetics and the thermodynamic driving force between the solid and liquid states. Here, we use molecular dynamics simulations to elucidate the atomistic details of this competition, focusing on water properties in the interfacial region along the secondary prismatic direction. The crystal growth velocity is maximized when the efficiency of converting interfacial water molecules to ice, collectively known as the Attachment Kinetics, is greatest. We find water molecules that contact the intermediate ice layer in concave regions along the atomistically roughened surface are more likely to freeze directly. The increased roughening of the solid surface at large undercoolings consequently plays an important limiting role on the rate of ice growth, as water molecules are unable to integrate into increasingly deeper surface pockets. These results provide insights into the molecular mechanisms for self-assembly of solid phases that are important in many biological and atmospheric processes.